One of the problems with the current crop of photovoltaic solar cells is that they tend to get less efficient as they get hotter. Most solar cells can only use specific wavelengths of the light – the unused frequencies don’t get used and instead generate heat. It gets even worse when you have concentrating solar cells (CSPs) – even more of the energy gets wasted as heat, and you need to have methods to try to keep the solar cells cool, because once regular solar cells hit 100 degrees C, they stop working. The PETE process uses this heat, instead of it going to waste. The Stanford researchers, led by Nick Melosh, an associate professor of materials science and engineering, are using a process called thermionic energy conversion that was actually first developed in the 1950’s, as NASA and the Soviet Space Agency worked to develop generators for space missions. What the Stanford researchers have done is combine this heat using process with the semiconductors used in solar cells. By coating a piece of semiconducting material with a thin layer of cesium, the cell was able to generate electricity from both light and heat.

They’re finding that the hotter the cell gets, the better it is in converting the heat to electricity, and that the coating keeps the cell working at even higher temperatures – it doesn’t even reach peak efficiency until it hits 250 degrees C. This makes the PETE process better suited for large solar farms using concentrating arrays to focus the sun. The Stanford team feels that the PETE devices could reach as high as 60 percent efficiency.

The below video from Stanford and their press release go into more detail about their solar cell design.